Photovoltaic Devices and Photovoltaic Roofing Elements Including Granules, and Roofs Using Them

ABSTRACT

The present invention includes photovoltaic devices and photovoltaic roofing elements comprising a photovoltaic element having an active face and an operating wavelength range; a polymer structure having (a) a bottom surface disposed on the active face of the photovoltaic element and (b) a top surface; and a plurality of granules disposed on the top surface of the polymer structure. Roofs including the photovoltaic devices and photovoltaic roofing elements of the present invention may be configured to have an aesthetically desirable appearance while retaining high photovoltaic efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to photovoltaic devices. Thepresent invention relates more particularly to photovoltaic devices withaesthetic properties making them suitable for use in roofingapplications.

2. Technical Background

The search for alternative sources of energy has been motivated by atleast two factors. First, fossil fuels have become more and moreexpensive due to increasing scarcity and unrest in areas rich inpetroleum deposits. Second, there exists overwhelming concern about theeffects of the combustion of fossil fuels on the environment, due tofactors such as air pollution (from NO_(x), hydrocarbons and ozone) andglobal warming (from CO₂). In recent years, research and developmentattention has focused on harvesting energy from natural environmentalsources such as wind, flowing water and the sun. Of the three, the sunappears to be the most widely useful energy source across thecontinental United States; most locales get enough sunshine to makesolar energy feasible.

There are now available components that convert light energy intoelectrical energy. Such “photovoltaic cells” are often made fromsemiconductor-type materials such as doped silicon in either singlecrystalline, polycrystalline, or amorphous form. The use of photovoltaiccells on roofs is becoming increasingly common, especially as deviceperformance has improved. They can be used, for example, to provide atleast a fraction of the electrical energy needed for a building'soverall function, or can be used to power one or more particulardevices, such as exterior lighting systems.

Often perched on an existing roof in panel form, these photovoltaicelements are quite visible and generally not aesthetically pleasant.Photovoltaic elements generally have an overall black to purpleappearance and are generally protected by a thin transparent glass orplastic cover. However, these colors frequently do not work wellaesthetically with the rest of the roof. Nonetheless, to date,installations have appeared to have been motivated by purely practicaland functional considerations; there appears to have been nocoordination between the appearance of the photovoltaic cells and theroofing materials (e.g., tiles or shingles) upon which they are mounted.Lack of aesthetic appeal is especially problematic in residentialbuildings with non-horizontally pitched roofs; people tend to put a muchhigher premium on the appearance of their homes than they do on theappearance of their commercial buildings. While there have been attemptsintegrate photovoltaic elements into more conventional roofingmaterials, none appear to have addressed the fact that the photovoltaicelement itself presents a generally aesthetically undesirable surface.

Accordingly, there remains a need for photovoltaic devices having morecontrollable and desirable aesthetics for use in roofing applicationswhile retaining sufficient efficiency in electrical power generation.

SUMMARY OF THE INVENTION

One aspect of the present invention is a photovoltaic device comprisinga photovoltaic element having an active face and an operating wavelengthrange; a polymer structure having a bottom surface disposed on theactive face of the photovoltaic element, and a top surface; and aplurality of granules disposed on the top surface of the polymerstructure.

Another aspect of the invention is a photovoltaic roofing elementincluding the above-described photovoltaic device.

Another aspect of the present invention is a photovoltaic roofingelement comprising a roofing substrate having a top face and a bottomface; a photovoltaic element disposed on the top face of or within theroofing substrate, leaving an exposed area on the top face of theroofing substrate, the photovoltaic element having an operatingwavelength range and an active face, the active face having an activearea and an inactive area; a polymer structure having a bottom surfacedisposed on the exposed area on the top face of the roofing substrate,and a top surface; and a plurality of granules disposed on the topsurface of the polymer structure.

Another aspect of the invention is a roof including one or more of theabove-described photovoltaic devices and/or photovoltaic roofingelements disposed on a roof deck.

Another aspect of the invention is an integrated granule productcomprising a polymer structure having a bottom surface and a topsurface; and a plurality of granules disposed on the top surface of thepolymer structure, wherein the combination of the granules and thepolymer structure has at least about 50% energy transmissivity of solarradiation in the 400-750 nm wavelength range, the 650-1000 nm wavelengthrange, or the 450-1150 nm wavelength range.

Another aspect of the invention is a method of modifying a surface of aphotovoltaic device, the method comprising disposing on the surface ofthe photovoltaic device a polymer structure, the polymer structurehaving a bottom surface and a top surface, the bottom surface beingdisposed on the surface of the photovoltaic device, the top surfacehaving granules disposed thereon.

The photovoltaic devices, photovoltaic roofing elements, roofs andmethods of the present invention result in a number of advantages overprior art methods. For example, the photovoltaic devices andphotovoltaic roofing elements of the present invention can be configuredto match, harmonize and/or complement a desired type of roofingmaterial. The roofs of the present invention can be aestheticallypleasing yet still generate significant photovoltaic power.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from the description or recognizedby practicing the invention as described in the written description andclaims hereof, as well as in the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings are not necessarily to scale,and sizes of various elements may be distorted for clarity. The drawingsillustrate one or more embodiment(s) of the invention, and together withthe description serve to explain the principles and operation of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a photovoltaic device according toone embodiment of the present invention;

FIG. 2 is a graph showing the relative spectral response of threesilicon-based photovoltaic materials as well as the spectral content ofsolar radiation;

FIG. 3 is a cross-sectional view of a photovoltaic device having apolymer structure having multiple layers according to one embodiment ofthe present invention;

FIG. 4 is a top perspective view of a photovoltaic roofing element basedon an asphalt shingle according to one embodiment of the presentinvention;

FIG. 5 is a cross-sectional view of a single tab of the photovoltaicroofing element depicted in FIG. 4;

FIG. 6 is a top perspective view of a photovoltaic roofing elementaccording to another embodiment of the present invention;

FIG. 7 is a cross-sectional view of the region surrounding one of thephotovoltaic devices of the photovoltaic roofing element depicted inFIG. 6;

FIG. 8 is a cross-sectional view of a photovoltaic roofing elementaccording to another embodiment of the invention;

FIG. 9 is a cross-sectional view of a photovoltaic roofing elementaccording to another embodiment of the invention;

FIG. 10 is a cross-sectional view of a photovoltaic roofing elementhaving a second polymer structure according to another embodiment of theinvention;

FIG. 11 is a cross-sectional view of a photovoltaic roofing element inwhich the polymer structure and granules extend to cover the active areaof the photovoltaic element according to another embodiment of theinvention; and

FIG. 12 is a cross-sectional view of a granule-coated polymer structureaccording to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the invention is a photovoltaic device. One example of aphotovoltaic device according to this aspect of the invention is shownin schematic cross-sectional view in FIG. 1. Photovoltaic device 100includes a photovoltaic element 102, which has an active face 104 and anoperating wavelength range. Photovoltaic element 102 includes one ormore photovoltaic cells individually electrically connected so as tooperate as a single unit.

Photovoltaic element 102 may be based on any desirable photovoltaicmaterial system, such as monocrystalline silicon; polycrystallinesilicon; amorphous silicon; III-V materials such as indium galliumnitride; II-VI materials such as cadmium telluride; and more complexchalcogenides (group VI) and pnicogenides (group V) such as copperindium diselenide. For example, one type of suitable photovoltaicelement includes an n-type silicon layer (doped with an electron donorsuch as phosphorus) oriented toward incident solar radiation on top of ap-type silicon layer (doped with an electron acceptor, such as boron),sandwiched between a pair of electrically-conductive electrode layers.As the skilled artisan will appreciate, other photovoltaic materialsystems can be used in the photovoltaic elements of the presentinvention. Photovoltaic element 102 may also include structural featuressuch as a substrate (e.g., an ETFE or polyester backing, a glass plate,or an asphalt non-woven glass reinforced laminate such as those used inthe manufacture of asphalt roofing shingles); one or more protectant orencapsulant materials (e.g., ETFE or EVA); one or more coveringmaterials (e.g., glass or plastic); mounting structures (e.g., clips,holes, or tabs); and one or more optionally connectorized electricalcables. Thin film photovoltaic materials and flexible photovoltaicmaterials may be used in the construction of photovoltaic elements foruse in the present invention. In one desirable embodiment of theinvention, the photovoltaic element is a monocrystalline silicon elementor a polycrystalline silicone photovoltaic element.

Photovoltaic element 102 desirably includes at least one antireflectioncoating, disposed on, for example, the very top surface of thephotoelectric element or between individual protectant, encapsulant orcovering layers.

Suitable photovoltaic elements may be obtained, for example, from ChinaElectric Equipment Group of Nanjing, China, as well as from severaldomestic suppliers such as Uni-Solar, Sharp, Shell Solar, BP Solar,USFC, FirstSolar, General Electric, Schott Solar, Evergreen Solar andGlobal Solar.

Active face 104 of photovoltaic element 102 is the face presenting thephotoelectrically-active areas of its one or more photoelectric cells.The active face may be the top surface of the one or more photovoltaiccells themselves, or more preferably may be the top surface of a seriesof one or more protectant, encapsulant and/or covering materialsdisposed thereon, as described above. As the skilled artisan willappreciate, during use of the photovoltaic device 100, active face 104should be oriented so that it is illuminated by solar radiation, and anymaterial covering it should be substantially non-opaque to radiationwithin the operating wavelength range of the photovoltaic element.

The photovoltaic element 102 also has an operating wavelength range.Solar radiation includes light of wavelengths spanning the near UV, thevisible, and the near infrared spectra. As used herein, when the term“solar radiation” is used without further elaboration, it is meant tospan the wavelength range of 300 nm to 1500 nm. As the skilled artisanwill appreciate, different photovoltaic elements have different powergeneration efficiencies with respect to different parts of the solarspectrum. FIG. 2 is a graph showing the relative spectral response ofthree commonly-used photovoltaic materials as well as the spectraldistribution of solar radiation. As the skilled artisan will recognize,amorphous doped silicon is most efficient at visible wavelengths, andpolycrystalline doped silicon and monocrystalline doped silicon are mostefficient at near-infrared wavelengths. As used herein, the operatingwavelength range of a photovoltaic element is the wavelength range overwhich the relative spectral response is at least 10% of the maximalspectral response. According to certain embodiments of the invention,the operating wavelength range of the photovoltaic element falls withinthe range of about 300 nm to about 2000 nm. Preferably, the operatingwavelength range of the photovoltaic element falls within the range ofabout 300 nm to about 1200 nm. For example, for photovoltaic deviceshaving photovoltaic cells based on typical amorphous silicon materialsthe operating wavelength range is between about 375 nm and about 775 nm;for typical polycrystalline silicon materials the operating wavelengthrange is between about 600 nm and about 1050 nm; and for typicalmonocrystalline silicon materials the operating wavelength range isbetween about 425 nm and about 1175 nm.

As shown in FIG. 1, photovoltaic device 100 also includes a polymerstructure 108. Polymer structure 108 has a bottom surface 110 disposedon the active face 104 of the photovoltaic element 102, and a topsurface 112. The polymer structure may be formed from, for example, asingle layer of a polymeric material, or multiple layers of polymericmaterials. According to one embodiment of the invention, the polymerstructure has an energy transmissivity to solar radiation of at leastabout 50% over the operating wavelength range of the photovoltaicelement. As used herein, an “energy transmissivity to solar radiation ofat least about 50% over the operating wavelength range of [a]photovoltaic element” means that at least about 50% of the total energyis transmitted when solar radiation within the operating wavelengthrange illuminates the polymer structure. The energy transmissivity ateach wavelength in the operating wavelength range need not be at leastabout 50%. Desirably, the polymer structure has at least about 75%energy transmissivity to solar radiation over the operating wavelengthrange of the photovoltaic element. In certain especially desirableembodiments of the invention, the polymer structure has at least about90% energy transmissivity to solar radiation over the operatingwavelength range of the photovoltaic element. The skilled artisan willrecognize that both the bulk properties and the thickness(es) of thematerial(s) of the polymer structure will influence the energytransmissivity of the polymer structure. In one embodiment of theinvention, the polymer structure has a thickness from about 50 μm toabout 2 mm. In certain desirable embodiments of the invention, thepolymer structure has a thickness from about 75 μm to about 1 mm.

The polymer structure may be, for example, a single layer of polymer.The polymer structure may alternatively include multiple layers.Desirably, the layer distal to the active face of the photovoltaicelement is an adhesive layer capable of adhering the granules to the topsurface of the polymer structure. For example, as shown in FIG. 3, thepolymer structure 308 may include three layers, including a structuralsupporting layer 314 (e.g., a 6-7 mil (˜150-175 μm) thick PET film); anadhesive layer 316 formed between the structural supporting layer 314and the active face 304 of the photovoltaic element 302; and an adhesivelayer 318 distal from the active face 304 of the photovoltaic element302. As the skilled artisan will recognize, the polymer structure mayhave other numbers of layers. For example, it may have a two layerstructure: a structural supporting layer, which is affixed to apolymeric protectant or encapsulant material of the photovoltaic elementusing heat and pressure; and an adhesive layer formed thereon. In someembodiments of the invention, the polymer structure on which thegranules, described below, are disposed is the polymeric protectant,encapsulant and/or covering layer(s) formed on top of the photovoltaiccell(s) of the photovoltaic element itself. Other than the granules,described below, the polymer structure is desirably substantially freeof particulate matter. In some embodiments of the invention, the polymerstructure has a substantially flat top surface. However, in otherembodiments of the invention, the top surface of the polymer structureis not substantially flat. For example, the top surface of the polymerstructure may have a patterned surface relief, or may have a roughenedsurface relief. As the skilled artisan will appreciate, surface reliefon the top surface of the polymer structure may be formed using standardtechniques such as embossing or casting.

The top layer of the polymer structure (i.e., the layer distal from thephotovoltaic cell(s)) is desirably an adhesive layer capable of adheringthe granules, described below, to the top surface of the polymerstructure. For example, the skilled artisan may use a two-part epoxy, ahot-melt thermoplastic, a heat-curable material or a radiation-curablematerial to form the adhesive layer. One particular example of apolymeric adhesive is the UV-cured product of a formulation consistingessentially of an acrylated urethane oligomer (e.g., EBECRYL 270,available from UCB Chemicals) with 1 wt % photoinitiator (e.g., IRGACURE651 from Ciba Additives). Other suitable adhesive materials includeethylene-acrylic acid and ethylene-methacrylic acid copolymers,polyolefins, PET, polyamides and polyimides. Examples of suitablematerials are described in U.S. Pat. Nos. 4,648,932, 5,194,113.5,491,021 and 7,125,601, each of which is hereby incorporated herein byreference.

According to another embodiment of the invention, the polymer structureis colored, but has at least about 50% energy transmissivity toradiation over the 750-1150 nm wavelength range. As used herein, an itemthat is “colored” is one that appears colored (including white, black orgrey, but not colorless) to a human observer. According to oneembodiment of the invention, the polymer structure includes (either atone of its surfaces or within it) a near infrared transmissivemultilayer interference coating designed to reflect radiation within adesired portion of the visible spectrum. In another embodiment of theinvention, the polymer structure includes (either at one of its surfacesor within it) one or more colorants (e.g., dyes or pigments) that absorbat least some visible radiation but substantially transmit near-infraredradiation. The color(s) and distribution of the colorants may beselected so that the photovoltaic device has an appearance that matches,harmonizes with and/or complements a desired type of roofing material,such as asphalt shingles of a given color and design. The pattern ofcolorant may be, for example, uniform, or may be mottled in appearance.Ink jet printing, lithography, or similar technologies may be used toprovide a pattern of colorant that approximates the appearance of theroofing materials to be used in conjunction with the photovoltaic device(e.g., granule-coated asphalt shingles). The polymer structure mayinclude a pattern of colorant at, for example, the bottom surface of thepolymer structure, the top surface of the polymer structure, or formedwithin the polymer structure. Desirably, when the polymer structure iscolored, the majority of the operating range of the photovoltaic elementis not within the 400-700 nm wavelength range.

Embodiments of the present invention having colored polymer structuresare especially useful with photovoltaic elements having most of theirphotovoltaic activity in the near infrared, such as those based onpolycrystalline silicon and monocrystalline silicon materials. Inembodiments of the invention having colored polymer structures, the useof granules can provide an aesthetically desirable rough surface to thephotovoltaic device, allowing it to more closely match a desired roofingmaterial (e.g., an asphalt roofing shingle). Photovoltaic devices madewith colored polymer structures are described in further detail in U.S.patent application Ser. No. 11/456,200, filed on Jul. 8, 2006 andentitled “Photovoltaic Device,” which is hereby incorporated herein byreference.

The photovoltaic devices according to this aspect of the invention alsoinclude a plurality of granules disposed on the top surface of thepolymer structure. In the embodiments of the invention demonstrated inFIGS. 1 and 3, a plurality of granules 120 and 320 are disposed on thetop surfaces 112 and 312 of the polymer structures 108 and 308,respectively. In certain embodiments of the invention, the granules arepartially embedded in the top surface of the polymer structure, as shownin FIGS. 1 and 3.

As will be described in more detail below, the granules may be made ofmany different materials and take many different forms. As the skilledartisan will appreciate, the granules may be small particles, oralternatively may be more similar to gravel in size. Regardless of theidentity of the granules, however, in certain embodiments of theinvention, the granule type, the physical distribution of the granules,and the polymer structure are selected so that the combination of thepolymer structure and the granules disposed thereon have an overallenergy transmissivity to radiation (preferably solar) of at least about40% over the operating wavelength range of the photovoltaic element.Desirably, the combination of the polymer structure and the granulesdisposed thereon have an overall energy transmissivity to radiation(preferably solar) of at least about 60% over the operating wavelengthrange of the photovoltaic element. In certain especially desirableembodiments of the invention, the combination of the polymer structureand the granules disposed thereon have an overall energy transmissivityto radiation (preferably solar) of at least about 80% over the operatingwavelength range of the photovoltaic element.

In certain embodiments of the invention, the granules have a size in therange of 0.2 mm to 3 mm (taken in their greatest dimension). In otherembodiments of the invention, the granules have a size in the range of0.4 mm to 2.4 mm (e.g., about 1 mm). The granules may be roughlyspherically symmetrical in shape (i.e., height˜length˜width), or may bemore planar in shape (i.e., length˜width>height).

According to one embodiment of the invention, the granules aresubstantially opaque to solar radiation over the operating wavelengthrange of the photovoltaic element. For example, the granules may haveless than 10% energy transmissivity to solar radiation over theoperating wavelength range of the photovoltaic element. Such granulesmay be made from virtually any material that will withstand exposure tothe environment without substantially degrading over a period of 10-20years, e.g., for example, rock, mineral, gravel, sand, ceramic, orplastic. In certain especially desirable embodiments of the invention,the granules are ceramic-coated mineral core particles optionallycolored with metal oxides, such as those used on asphalt roofingshingles. The mineral core can consist of any chemically inert matterthat can support a ceramic layer and has adequate mechanical properties.For example, the mineral core can be formed from materials available inthe natural state, such as talc, granite, siliceous sand, andesite,porphyry, marble, syenite, rhyolite, diabase, quartz, slate, basalt,sandstone, and marine shells, as well as material derived from recycledmanufactured goods, such as bricks, concrete, and porcelain.

When the granules are substantially opaque to radiation, they aredesirably disposed on the top surface of the polymer structure with asurface fill factor of no greater than about 75% over the active face ofthe photovoltaic element. The surface fill factor is the fraction of theactive face of the photovoltaic element that is occluded by thegranules, as measured in a direction normal to the active face of thephotovoltaic element. Desirably, the granules have a surface fill factorof no greater than about 50%. In certain desirable embodiments of theinvention, the granules have a surface fill factor of no greater thanabout 25%. The color(s) and distribution of the granules may random oras selected by the skilled artisan so that the photovoltaic device hasan appearance that matches, harmonizes with and/or complements a desiredtype of roofing material, such as asphalt shingles of a given color anddesign.

According to another embodiment of the invention, the granules are atleast partially transmissive to radiation (preferably solar) over theoperating wavelength range of the photovoltaic element. For example, inone embodiment of the invention, the partially transmissive granuleshave at least about 50% energy transmissivity to radiation (preferablysolar) over the operating wavelength range of the photovoltaic element.Desirably, the partially transmissive granules have at least about 75%energy transmissivity to radiation (preferably solar) over the operatingwavelength range of the photovoltaic element. In certain especiallydesirable embodiments of the invention, the partially transmissivegranules have at least about 90% energy transmissivity to radiation(preferably solar) over the operating wavelength range of thephotovoltaic element. At least partially transmissive granules can beformed from glass, such as in the form of cullet or beads. At leastpartially transmissive granules can also be formed from, for example,from quartz, sand, non-vitreous ceramics such as those described in U.S.Pat. Nos. 4,349,456, 4,565,556 and 4,605,594, each of which is herebyincorporated herein by reference, or polymeric materials such aspolypropylene, poly(ethylene terephthalate), poly(propylene oxide),acrylic polymers, or polysulfone. The partially transmissive granulesmay be treated with an adhesion promoter in order to enhance theiradhesion to the top surface of the polymer structure. In certaindesirable embodiments of the invention, the partially transmissivegranules are coated with an anti-reflective layer (e.g., using fluidizedbed coating processes such as those described in U.S. Patent ApplicationPublication no. 2006/0251807, which is hereby incorporated herein byreference, and/or conventional pan-coating processes). Desirably, thepartially transmissive granules have an index of refraction that isclosely matched to the index of refraction of the polymeric structure atits top surface. For example, the difference between the n_(D) value ofthe partially transmissive granule and the n_(D) value of the polymericstructure at its top surface is desirably less than about 0.1, and moredesirably less than about 0.05. In certain embodiments of the invention,the partially transmissive granules are substantially spherical inshape, so as to function as lenses guiding light to the active face ofthe photovoltaic element.

Because the granules according to this embodiment transmit radiation,they may generally be disposed on the polymer structure with much highersurface fill factors compared to opaque granules. For example, accordingto one embodiment of the invention, the partially transmissive granuleshave a surface fill factor of greater than about 50%. In certaindesirable embodiments of the invention, the partially transmissivegranules have a surface fill factor of greater than about 75%. The useof partially transmissive granules can provide surface relief to aphotovoltaic device, providing more desirable aesthetic qualities whencompared with the generally flat surface of a conventional photovoltaicdevice.

According to another embodiment of the invention, at least some of thegranules are opaque to at least some visible radiation, but have atleast about 50% energy transmissivity of radiation over the 750-1150 nmwavelength range. Such granules may be, for example, partiallytransmissive granules (as described above) coated with a near infraredtransmissive coating. The near infrared transmissive coating may be, forexample, a polymeric ink having a colorant (e.g., a dye or a pigment)that absorbs visible radiation. Alternatively, the near infraredtransmissive coating may be a multilayer interference coating designedto reflect a radiation within a desired portion of the visible spectrum.Pigments with high near infrared transmissivity include pearlescentpigments, light-interference platelet pigments, ultramarine blue,ultramarine purple, cobalt chromite blue, cobalt aluminum blue, chrometitanate, nickel titanate, cadmium sulfide yellow, cadmium sulfoselenideorange, and organic pigments such as phthalo blue, phthalo green,quinacridone red, diarylide yellow, and dioxazine purple. The color(s)and distribution of the infrared transmissive granules may be selectedso that the photovoltaic device has an appearance that matches,harmonizes with, and/or complements a desired type of roofing material,such as granule-coated asphalt shingles of a given color and design.Desirably, when the granules are colored, the majority of the operatingrange of the photovoltaic is not within the 400-700 nm wavelength range.Embodiments of the present invention having colored granules areespecially useful with photovoltaic elements having operating wavelengthranges that include the near-infrared, such as those based onpolycrystalline silicon and monocrystalline silicon materials.

It may be desirable to use more than one type of granule in thephotovoltaic devices of the present invention. For example, in someembodiments of the invention, a mixture of opaque and at least partiallytransmissive granules are used in order to achieve a desired balance ofappearance and transmissivity. Of course, as the skilled artisan wouldappreciate, multiple colors of granules may also be used to achieve adesired aesthetic effect. Similarly, different zones of the photovoltaicdevice may be covered with granules of different composition, colorand/or distribution. For example, the active area of the active face ofthe photovoltaic element might be covered with granules of onecolor/composition/distribution, while the remainder of the device iscovered with granules of another color/composition/distribution. Usingdifferent granules in different zones allows the skilled artisan tomaximize transmission of solar radiation to the active area, whilemaintaining a desirable appearance and cost for the overall device. U.S.Patent Application Publication no. 2006/0260731, which is herebyincorporated herein by reference, describes methods useful in themanufacture of multi-granule roofing materials; these methods can beadapted by the skilled artisan for use in the present invention.

When the photovoltaic device is relatively thick, it may be desirablefor the polymer structure and the granules disposed thereon to cover notonly its active face, but also one or more of its edge faces, so as toimpart to it a desired appearance when it is installed on a roof. Theedge faces would be especially visible when the photovoltaic device isinstalled on a non-horizontally pitched roof; accordingly, when such aninstallation is contemplated it may be especially desirable to cover oneor more edge faces of the photovoltaic element with a polymer structureand granules substantially as described herein.

One or more of the photovoltaic devices described above may be installedon a roof as part of a photovoltaic system for the generation ofelectric power. Accordingly, one aspect of the invention is a roofcomprising one or more photovoltaic devices as described above disposedon a roof deck. The photovoltaic devices are desirably connected to aphotovoltaic system, either in series, in parallel, or inseries-parallel, as would be recognized by the skilled artisan.

Because the photovoltaic devices of the present invention are desirablyused on a roof, it may be desirable to incorporate them with a roofingmaterial. Accordingly, one aspect of the invention is a photovoltaicroofing element comprising one or more photovoltaic devices as describedabove disposed on or within a roofing substrate. Roofing substratessuitable for use in this aspect of the invention include, for example,shingles, tiles, panels, membranes and shakes. As used herein, aphotovoltaic device disposed “on” a roofing substrate is disposed on atop surface of the roofing substrate (as described below in more detailwith reference to FIGS. 4 and 5), while a photovoltaic device disposed“within” a roofing substrate is disposed on a bottom or side surface ofthe roofing substrate, with the active area of its photovoltaic elementbeing exposed to face the same direction as the top surface of theroofing substrate (as described below in more detail with reference toFIGS. 6 and 7).

Another embodiment of the invention is shown in perspective top view inFIG. 4, and in partial cross-sectional view in FIG. 5. Photovoltaicroofing element 430 includes four photovoltaic devices 400 substantiallyas described above, disposed on a roofing substrate 432. In theembodiment of the invention shown in FIGS. 4 and 5, the roofingsubstrate 432 is a dual-layer multi-tab asphalt roofing shingle; thecross-sectional view of FIG. 5 is of a single tab. In the embodiment ofthe invention shown in FIG. 4, each of the photovoltaic devices has apair of connectorized electrical cables 434 that remain disposed on topof the roofing substrate 432; they may be connected into an electricalsystem and covered by the tabs of the next course of shingles. Theskilled artisan will recognize that any electrical cables in thephotovoltaic elements may be routed in many different ways. For example,they can run through a hole in the roofing substrate and be potted in byroofing compound; or be integrated into the roofing substrate itself.The photovoltaic device may be attached to the roofing substrate usingadhesive (as demonstrated in FIG. 5 by adhesive layer 433), oralternatively may be screwed, clipped, or nailed to the roofingsubstrate or to the roof deck, as would be appreciated by the skilledartisan. The color(s) and distribution of the granules may be selectedby the skilled artisan so that the photovoltaic devices have anappearance that matches, harmonizes with and/or complements that of theasphalt roofing shingle.

While the embodiment of FIGS. 4 and 5 is based on an asphalt roofingshingle, the skilled artisan will appreciate that any desirable roofingsubstrate may be used in the photovoltaic roofing elements of thepresent invention. For example, in certain embodiments of the invention,the roofing substrate is a roofing membrane, a ceramic tile, or a metalpanel.

Another embodiment of the invention is shown in perspective top view inFIG. 6 and in cross-sectional view in FIG. 7. For simplicity, only aportion in the neighborhood of one of the photovoltaic elements is shownin FIG. 7. Photovoltaic roofing element 630 includes two photovoltaicdevices 600 substantially as described above disposed within a roofingsubstrate 632. In the embodiment of the invention shown in FIGS. 6 and7, the roofing substrate 632 is a two layer laminated asphalt roofingshingle, having a top layer 634 and a bottom layer 636. The photovoltaicdevices 600 have an exposed area 638, and recessed attachment surfaces640 along their three sides that are attached to roofing substrate 632.The top layer 634 of roofing substrate is affixed to the attachmentsurface 640, preferably in a watertight fashion using a suitableadhesive (e.g., asphalt, roofing compound). The bottom layer 636 of theroofing substrate is desirably roughly equivalent in thickness to theattachment surface 640 so that the top layer 634 of the roofingsubstrate 632 appears relatively flat. The entire area of the exposedarea 638 is desirably covered with granules. The color(s) anddistribution of the granules may be selected by the skilled artisan sothat the photovoltaic devices have an appearance that matches,harmonizes with and/or complements that of the asphalt roofing shingle.

While the embodiments described with reference to FIGS. 4-7 havetwo-layer shingles as their roofing substrates, the skilled artisan willappreciate that more or fewer layers may used. For example, more layersmay help improve stability and help better accommodate the thickness ofthe photovoltaic element. As the skilled artisan will appreciate,additional layers (and partial layers) of shingle material may be usedfor other purposes, such as to meet aesthetic, mechanical, orweatherproofness requirements. Of course, a single layer of asphaltshingle material may be used as the roofing substrate.

Another aspect of the invention is a photovoltaic roofing element asshown in cross-sectional view in FIG. 8. Photovoltaic roofing element830 includes a roofing substrate 832 having a top face 852 and a bottomface 854. The roofing substrate may be, for example, an asphaltnon-woven glass reinforced laminate (e.g., an asphalt roofing shinglewithout the conventional top layer of ceramic-coated inorganicgranules). A photovoltaic element 802 is disposed on the top face 852 ofthe roofing substrate 832, leaving an exposed area 856 (i.e., notcovered by the photovoltaic element) on the top face 852 of the roofingsubstrate 832. The photovoltaic element may also be disposed within theroofing substrate, as described above. Desirably, the photovoltaicelement includes near its top surface at least one waterproofprotectant, encapsulant or covering layer. The photovoltaic element 802has an active face 804 and an operative wavelength range, as describedabove. The active face 804 has an active area 858 and an inactive area860. The active area is the area over which incident light can causephotovoltaic power generation (i.e., where the photovoltaic cells arepresented), and the inactive area is any area over which incident lightcannot cause photovoltaic power generation. Polymer structure 808,substantially as described above, has a bottom surface 810 disposed onthe exposed area 856 of the top face 852 of the roofing substrate 832,as well as a top surface 812. A plurality of granules 820 are disposedon the top surface 812 of the polymer structure 808. In the embodimentof FIG. 8, the granules 820 and the polymer structure 808 need nottransmit light in the operating wavelength range of the photovoltaicdevice, and therefore may be formed from any desirable material, asdescribed in further detail below.

According to one embodiment of the invention, the granules disposed onthe top surface of the polymer structure over the exposed area of theroofing substrate are desirably substantially opaque to ultravioletradiation and are colored. When the roofing substrate is an asphaltnon-woven glass reinforced laminate having no other granules thereon,granules that are opaque to ultraviolet radiation and are colored canhelp prevent the photodegradation of the asphalt material, as would beappreciated by the skilled artisan. For example, the granules may besubstantially opaque to solar radiation. Such granules may be made from,for example, rock, mineral, gravel, sand, ceramic, or plastic. Incertain especially desirable embodiments of the invention, the granulesare ceramic-coated mineral particles optionally colored with metaloxides, such as those used on conventional asphalt roofing shingles.Alternatively, the granules may be colored, but have at least about 50%energy transmissivity of solar radiation over the 750-1150 nm wavelengthrange, as described above. When the granules are substantially opaque toultraviolet radiation and are colored, they desirably have a surfacefill factor of greater than about 50%. In certain desirable embodimentsof the invention, the granules have a surface fill factor of greaterthan about 75%.

According to another embodiment of the invention, the polymer structureitself is substantially opaque to ultraviolet radiation and is colored.The polymer structure may be substantially opaque to solar radiation,and may be based on, for example, a pigmented polymer sheet.Alternatively, the polymer structure may be a colored polymer structureas described above.

In certain embodiments of the invention, the polymer structure does notextend to cover the active area of the active face of the photovoltaicelement. It may, however, extend to cover at least part of the inactivearea of the active face of the photovoltaic element. As shown incross-sectional view in FIG. 9, polymer structure 908 and granules 920cover not only the exposed area 956 of the top surface 952 of theroofing substrate, but also most of the inactive area 960 of the activeface 904 of the photovoltaic element 902. The granules 920 do not coverthe active area 958 of the active face 904 of the photovoltaic element902. In the embodiment of FIG. 9, the photovoltaic element 902 isembedded in the top surface 952 of the roofing substrate 932. Inembodiments of the invention in which the polymer structure does notcover the active area of the active face of the photovoltaic element, itmay be desirable to use polymer structures and/or granules that aresubstantially opaque to ultraviolet radiation and are colored, asdescribed above.

When the polymer structure does not extend to cover the active area ofthe active face of the photovoltaic element, it may be desirable for thephotovoltaic element to have its own polymer structure and granulesdisposed on it, substantially as described above. For example, FIG. 10is a cross-sectional view of a photovoltaic roofing element 1030, inwhich photovoltaic element 1002 has an active face 1004. Photovoltaicroofing element 1030 also includes a roofing substrate 1032, a polymerstructure 1008, and a plurality of granules 1020 substantially asdescribed above with reference to FIG. 8. A second polymer structure1066 has a bottom surface 1068 disposed on the active face 1004 of thephotovoltaic element 1002, and a top surface 1070. The photovoltaicroofing element 1030 further includes a second plurality of granules1072 disposed on the top surface 1070 of the second polymer structure1066. As shown in FIG. 10, the second polymer structure and secondplurality of granules may cover the entire active face of thephotovoltaic element. Alternatively, in another embodiment of theinvention, the second polymer structure covers only the active area ofthe active face of the photovoltaic element, with the polymer structurethat is disposed on the exposed face of the roofing element extending tocover any inactive area as described above with reference to FIG. 9. Inthe embodiment of FIG. 10, the granules 1020 and the polymer structure1008 need not transmit light in the operating wavelength range of thephotovoltaic device, and therefore may be formed from any desirablematerial, as described above.

When the photovoltaic roofing element includes a second plurality ofgranules 1072, they desirably have the properties described above withrespect to the photovoltaic devices according to the first aspect of theinvention (e.g., FIGS. 1 and 3-7). For example, in one embodiment of theinvention the granules of the second plurality of granules aresubstantially opaque to radiation over the operating wavelength range ofthe photovoltaic element, and have a surface fill factor of no greaterthan about 75% over the active face of the photovoltaic element.Desirably, they have a surface fill factor of no greater than about 50%,and in certain especially desirable embodiments of the invention, theyhave a surface fill factor of no greater than about 25%. The opaquegranules may be, for example, ceramic-coated inorganic particles. Inanother embodiment of the invention, the granules are at least partiallytransmissive to radiation over the operating wavelength range of thephotovoltaic element. For example, the granules may transmit at leastabout 50% or at least about 75% of radiation (preferably solar) over theoperating wavelength range of the photovoltaic element. Such partiallytransmissive granules may be made from, for example, quartz, sand, glass(e.g., in the form of cullet or beads), non-vitreous ceramics, such asthose described in U.S. Pat. Nos. 4,349,456, 4,565,556 and 4,605,594,each of which is hereby incorporated herein by reference, or polymericmaterials such as polypropylene, poly(ethylene terephthalate),poly(propylene oxide), acrylic polymers, or polysulfone. In anotherembodiment of the invention, the partially transmissive granules areopaque to at least some visible radiation but have at least about 50%energy transmissivity to radiation (preferably solar) over the 750-1150nm wavelength range. Such granules may be, for example, substantiallytransparent particles having IR-transmissive coatings. The granules ofthe second plurality of granules desirably have a size in the range of0.2 mm to 3 mm (taken in their greatest dimension). In other embodimentsof the invention, the granules of the second plurality of granules havea size in the range of 0.4 mm to 2.4 mm (e.g., about 1 mm). Thesegranules may be roughly spherically symmetrical in shape (i.e.,height˜length˜width), or may be more planar in shape (i.e.,length˜width>height).

When the photovoltaic roofing element includes a second polymerstructure, it desirably has the properties described above with respectto the photovoltaic devices according to the first aspect of theinvention (e.g., FIGS. 1 and 3-7). For example, the second polymerstructure may be a single layer of polymer adhesive, or include multiplelayers. The second polymer structure desirably has an energytransmissivity of at least about 50%, at least about 75%, or at leastabout 90% over the operating wavelength range of the photovoltaicelement. The second polymer structure desirably has a thickness of fromabout 50 μm to about 2 mm, or from about 75 μm to about 1 mm. In anotherembodiment of the invention, the second polymer structure is colored buthas at least about 50% energy transmissivity of solar radiation in the750-1150 nm wavelength range. Desirably, the combination of the secondpolymer structure and the granules disposed thereon has an overallenergy transmissivity to radiation (preferably solar) of at least about40%, at least about 60%, or at least about 80% over the operatingwavelength range of the photovoltaic element.

According to another embodiment of the invention, shown in FIG. 11, thepolymer structure extends to cover the active area of the active face ofthe photovoltaic element as well as the exposed area of the roofingsubstrate. In FIG. 11, photovoltaic roofing element 1130 includes aphotovoltaic element 1102, and a roofing substrate 1132 as describedabove with respect to FIG. 9. Photovoltaic roofing element 1130 alsoincludes a polymer structure 1108 that extends to cover not only theexposed area of the roofing substrate, but also the entire active face1104 of the photovoltaic element 1102. A plurality of granules 1120 isdisposed on the top face of the polymer structure 1108 over its entirearea. In one embodiment of the invention, the granules disposed on thepolymer structure above the active area of the active face of thephotovoltaic element have substantially the same composition and surfacefill factor as the granules disposed on the polymer structure above theroofing substrate.

When the polymer structure extends over the active area of the activeface of the photovoltaic element, it desirably has the propertiesdescribed above with respect to the second polymer structure. When thegranules are disposed on the polymer structure over the active area ofthe photovoltaic element, they desirably have the properties describedabove with respect to the second plurality of granules.

In the embodiment of FIG. 11, the plurality of granules is disposed onthe polymer structure over its entire top face. However, in otherembodiments, the granules may be disposed on only on parts of the topface of the polymer structure. For example, in one embodiment of theinvention, granules are disposed on the top face of the polymerstructure over the exposed area of the roofing substrate, but not overthe active area of the active face of the photovoltaic element. In suchcases, the polymer structure is desirably colored in the area of theactive area. The identity and distribution of the color(s) in the areaof the active area may be selected by the skilled artisan to match,harmonize and/or complement the appearance of the granule-coated polymerstructure disposed over the exposed area of the roofing substrate.

In another embodiment of the invention, the granules disposed on thepolymer structure over the active area of the photovoltaic element aredifferent in color distribution, surface fill factor, and/or compositionthan the granules disposed on the polymer structure over the exposedarea of the roofing substrate. The colors, composition and distributionof the granules may be chosen by the skilled artisan so that theappearance of the active face of the photovoltaic element matches,harmonizes with and/or complements that of the exposed area of theroofing substrate.

For example, in one embodiment of the invention, the granules disposedon the polymer structure over the active area of the photovoltaicelement are glass cullet; and the granules disposed on the polymerstructure over the exposed area of the roofing substrate areceramic-coated inorganic granules with a surface fill factor of greaterthan about 50%. In this embodiment of the invention, the polymerstructure over the active area of the photovoltaic element is desirablycolored so that it matches, harmonizes with, and/or complements theappearance of the ceramic-coated granules disposed on the polymerstructure over the exposed area of the roofing substrate.

In the embodiments described above with reference to FIGS. 10 and 11,the granule color, composition and/or distribution can vary betweenzones on the photovoltaic roofing element. As described above, usingdifferent granules in different zones allows the skilled artisan tomaximize transmission of solar radiation to the active area, whilemaintaining a desirable appearance and cost for the overall device.

In another embodiment of the invention, the polymer structure provides acover for electrical cables connected to the photovoltaic element. Forexample, in one embodiment of the invention (e.g., as shown in FIG. 4),the photovoltaic roofing element includes one or more electrical cablesoperatively coupled to the photovoltaic element. These electrical cablesmay be used to interconnect individual photovoltaic elements within asingle photovoltaic roofing element, and/or interconnect one or morephotovoltaic roofing elements into a photovoltaic system. The cables mayoptionally be connectorized. The cables and any connectors desirablymeet UNDERWRITERS LABORATORIES (UL) and NATIONAL ELECTRICAL CODE (NEC)standards for safety. In certain embodiments of the invention, thecables and any connectors are selected to withstand loads of up to 600VDC at 2-10 amperes. The one or more electrical cables are at least inpart disposed between the top face of polymer structure and the top faceof the roofing substrate. In certain desirable embodiments of theinvention, the roofing substrate has a channel formed therein, and theone or more electrical cables are at least partially disposed in thechannel and are covered by the polymer structure. The polymer structuremay simply cover the one or more electrical cables, or may partially orcompletely encapsulate them.

The photovoltaic devices and photovoltaic roofing elements describedabove are generally installed as arrays of photovoltaic devices orphotovoltaic roofing elements. Accordingly, another aspect of theinvention is an array of photovoltaic devices or photovoltaic roofingelements as described above. As the skilled artisan will appreciate, thearray can include any desirable number of photovoltaic devices orphotovoltaic roofing elements, which can be arranged in any desirablefashion. For example, the array can be arranged as partiallyoverlapping, offset rows of photovoltaic devices or photovoltaic roofingelements, in a manner similar to the conventional arrangement of roofingmaterials. The photovoltaic devices or photovoltaic roofing elementswithin the array can be electrically connected in series, in parallel,or in series-parallel, as would be evident to the skilled artisan. Inone embodiment of the invention, the array of photovoltaic devices orphotovoltaic roofing elements is fixed in a frame system similar to thatused in conventional rooftop photovoltaic modules.

One or more of the photovoltaic devices and/or photovoltaic roofingelements described above may be installed on a roof as part of aphotovoltaic system for the generation of electric power. Accordingly,one aspect of the invention is a roof comprising one or morephotovoltaic devices as described above disposed on a roof deck. Anotheraspect of the invention is a roof comprising one or more photovoltaicroofing elements as described above disposed on a roof deck. Thephotovoltaic elements of the photovoltaic devices and/or photovoltaicroofing elements are desirably connected to a photovoltaic system,either in series, in parallel, or in series-parallel, as would berecognized by the skilled artisan. Electrical connections are desirablymade using cables, connectors and methods that meet UL and NECstandards.

Photovoltaic roofing elements of the present invention may be fabricatedusing many techniques familiar to the skilled artisan. The polymerstructures may be fabricated, for example, using the methods describedin U.S. Pat. Nos. 5,194,113 and 7,125,601, or using doctor blading,laminating, and/or molding techniques familiar to the skilled artisan.For example, when the roofing substrate is an asphalt shingle or anasphalt non-woven glass reinforced laminate, the methods described inU.S. Pat. Nos. 5,953,877; 6,237,288; 6,355,132; 6,467,235; 6,523,316;6,679,308; 6,715,252; 7,118,794; U.S. Patent Application Publication2006/0029775; and International Patent Application Publication WO2006/121433. Each of the patents and publications referenced above ishereby incorporated herein by reference in its entirety. Photovoltaicroofing elements may be fabricated in a continuous process and then cutinto individual elements as is done in the fabrication of asphaltshingles. When a continuous process is used, it may be necessary toindividually prepare any electrical cables running between elements, forexample by cutting the cables between elements and connectorizing thecut ends.

Another aspect of the invention is a granule-coated polymer structure,an example of which is shown in cross-sectional view in FIG. 12.Granule-coated polymer structure 1280 includes a polymer structure 1208having a top surface 1212 and a bottom surface 1210. The top surface1212 has a plurality of granules 1220 disposed on it, as described abovewith respect to the photovoltaic devices and photovoltaic roofingelements of the present invention. The polymer structure and theplurality of granules are chosen so that their combination has at leastabout 40% energy transmissivity of radiation over the 400-750 nmwavelength range, the 650-1000 nm wavelength range, or the 450-1150 nmwavelength range. Granule-coated polymer structures according to thisaspect of the invention may be useful in manufacturing roofing elements,as described above. Granule-coated polymer structures according to thisaspect of the invention may be fabricated, for example, using themethods described in U.S. Pat. Nos. 5,194,113 and 7,125,601, as well asthose familiar to the skilled artisan.

The polymer structure desirably has the properties described above withrespect to the photovoltaic devices according to the first aspect of theinvention. For example, the polymer structure may be a single layer ofpolymer, or include multiple layers. The polymer structure desirably hasan energy transmissivity of at least about 50%, at least about 75%, orat least about 90% over the operating wavelength range of thephotovoltaic element. The polymer structure desirably has a thickness offrom about 50 μm to about 2 mm, or from about 75 μm to about 1 mm. Inanother embodiment of the invention, the polymer structure is coloredbut has at least about 50% energy transmissivity of radiation in the750-1150 nm wavelength range.

The granules desirably have the properties described above with respectto the photovoltaic devices according to the first aspect of theinvention. For example, in one embodiment of the invention the granulesare substantially opaque to radiation over the operating wavelengthrange of the photovoltaic element, and have a surface fill factor of nogreater than about 75% over the active face of the photovoltaic element.Desirably, they have a surface fill factor of no greater than about 50%,and in certain especially desirable embodiments of the invention, theyhave a surface fill factor of no greater than about 25%. The opaquegranules may be, for example, ceramic-coated inorganic particles. Inanother embodiment of the invention, the granules are at least partiallytransmissive to radiation over the operating wavelength range of thephotovoltaic element. For example, the granules may transmit at leastabout 50% or at least about 75% of solar radiation over the operatingwavelength range of the photovoltaic element. Such granules may be madefrom, for example, quartz, sand, glass (e.g., in the form of cullet orbeads), non-vitreous ceramics, such as those described in U.S. Pat. Nos.4,349,456, 4,565,556 and 4,605,594, each of which is hereby incorporatedherein by reference, or polymeric materials such as polypropylene,poly(ethylene terephthalate), poly(propylene oxide), acrylic polymers,or polysulfone. In another embodiment of the invention, the partiallytransmissive granules are colored but have at least about 50% energytransmissivity to solar radiation over the 750-1150 nm wavelength range.Such granules may be, for example, substantially transparent particleshaving IR-transmissive coatings. The granules desirably have a size inthe range of 0.2 mm to 3 mm.

Another aspect of the invention is a method of modifying a surface of aphotovoltaic device comprising disposing on the surface of thephotovoltaic device a polymer structure having granules disposedthereon. As the skilled artisan will appreciate, it may often bedesirable to have the appearance of a photovoltaic element match,harmonize and/or complement that of a roofing material. As describedabove, the color of the polymer structure and the color(s) of thegranules can be selected to provide a desirable appearance as well assufficiently high transmissivity to solar radiation. The granules can beadded to the polymer structure at any time (i.e., before, during orafter the attachment of the polymer structure to the photovoltaicdevice). As the skilled artisan will understand, the polymer structureand granules can be selected substantially as described above.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the scope of the invention. Thus, it is intendedthat the present invention cover the modifications and variations ofthis invention provided they come within the scope of the appendedclaims and their equivalents.

The following listing of claims will replace all prior versions andlistings of claims in the application.

1. A photovoltaic device comprising: a photovoltaic element having an active face and an operating wavelength range; a polymer structure having (a) a bottom surface disposed on the active face of the photovoltaic element and (b) a top surface; and a plurality of granules disposed on the top surface of the polymer structure.
 2. The photovoltaic device of claim 1, wherein the granules (a) are substantially opaque to radiation over the operating wavelength range of the photovoltaic element and (b) have a surface fill factor of no greater than about 75% over the active face of the photovoltaic element.
 3. (canceled)
 4. The photovoltaic device of claim 1, wherein the granules are at least partially transmissive to radiation over the operating wavelength range of the photovoltaic element.
 5. The photovoltaic device of claim 4, wherein the granules transmit at least about 50% of solar radiation over the operating wavelength range of the photovoltaic element.
 6. The photovoltaic device of claim 4, wherein the granules are made of glass.
 7. (canceled)
 8. The photovoltaic device of claim 4, wherein the granules are made of quartz, sand, a non-vitreous ceramic, or a polymeric material.
 9. The photovoltaic device of claim 4, wherein the granules are opaque to at least some visible radiation but have at least about 50% energy transmissivity to solar radiation over the 750-1150 nm wavelength range.
 10. (canceled)
 11. The photovoltaic device of claim 1, wherein the granules have a size in the range from about 0.2 mm to about 3 mm.
 12. The photovoltaic device of claim 1, wherein the polymer structure is a single layer of polymer.
 13. The photovoltaic device of claim 1, wherein the polymer structure comprises a plurality of layers, wherein the layer distal to the active face of the photovoltaic element is a layer of polymer capable of adhering the granules. 14-15. (canceled)
 16. The photovoltaic device of claim 1, wherein the polymer structure is colored but has at least about 50% energy transmissivity to solar radiation over the 750-1150 nm wavelength range. 17-18. (canceled)
 19. An array of photovoltaic devices of claim
 1. 20. A photovoltaic roofing element, comprising a photovoltaic device of claim 1, disposed on or within a roofing substrate.
 21. The photovoltaic roofing element of claim 20, wherein the roofing substrate is a roofing shingle, tile, panel, membrane or shake. 22-23. (canceled)
 24. An array of photovoltaic roofing elements of claim
 20. 25. A roof comprising one or more photovoltaic devices of claim 1 disposed on a roof deck.
 26. A photovoltaic roofing element comprising a roofing substrate having a top face and a bottom face; a photovoltaic element disposed on the top face of or within the roofing substrate, leaving an exposed area on the top face of the roofing substrate, the photovoltaic element having an operating wavelength range and an active face, the active face having an active area and an inactive area; a polymer structure having a bottom surface disposed on the exposed area on the top face of the roofing substrate, and a top surface; and a plurality of granules disposed on the top surface of the polymer structure.
 27. The photovoltaic roofing element of claim 26, wherein the polymer structure extends to cover the active area of the active face of the photovoltaic element.
 28. The photovoltaic roofing element of claim 27, wherein the granules disposed on the polymer structure above the active area of the active face of the photovoltaic element are (a) substantially opaque to radiation over the operating wavelength range of the photovoltaic element, and (b) have a surface fill factor of no greater than about 75%.
 29. The photovoltaic roofing element of claim 28, wherein the granules disposed on the polymer structure above the active area of the active face of the photovoltaic element are ceramic-coated mineral core particles.
 30. The photovoltaic roofing element of claim 27, wherein the granules disposed on the polymer structure above the active area of the active face of the photovoltaic element are not substantially opaque to radiation over the operating wavelength range of the photovoltaic element. 31-32. (canceled)
 33. The photovoltaic roofing element of claim 26, wherein the granules disposed on the polymer structure above the active area of the active face of the photovoltaic element have substantially the same composition and surface fill factor as the granules disposed on the polymer structure above the roofing substrate.
 34. The photovoltaic roofing element of claim 26, wherein the granules disposed on the polymer structure above the active area of the active face of the photovoltaic element have a substantially different color distribution, composition and/or surface fill factor as the granules disposed on the polymer structure above the roofing substrate.
 35. The photovoltaic roofing element of claim 26, wherein the polymer structure does not extend to cover the active area of the active face of the photovoltaic element.
 36. The photovoltaic roofing element of claim 35, wherein the granules are substantially opaque to ultraviolet radiation and are colored. 37-39. (canceled)
 40. The photovoltaic roofing element of claim 35, further comprising a second polymer structure having a bottom surface disposed on the active face of the photovoltaic element, and a top surface; and a second plurality of granules disposed on the top surface of the second polymer structure.
 41. The photovoltaic roofing element of claim 40, wherein the granules of the second plurality of granules are substantially opaque to radiation over the operating wavelength range of the photovoltaic element, and have a surface fill factor of no greater than about 75%.
 42. The photovoltaic roofing element of claim 40, wherein the granules of the second plurality of granules are not substantially opaque to radiation over the operating wavelength range of the photovoltaic element.
 43. (canceled)
 44. The photovoltaic roofing element of claim 26, wherein the photovoltaic element further comprises one or more electrical cables; and wherein the one or more electrical cables are disposed between the polymer structure and the roofing substrate.
 45. The photovoltaic roofing element of claim 44, wherein the roofing substrate has a channel formed in its top face, and wherein the one or more electrical cables are disposed within the channel and covered by the polymer structure.
 46. The photovoltaic roofing element of claim 26, wherein the roofing substrate is a roofing shingle, tile, panel, membrane or shake. 47-48. (canceled)
 49. A roof comprising one or more photovoltaic roofing elements according to claim 26 disposed on a roof deck.
 50. A granule coated polymer structure comprising: a polymer structure having a bottom surface and a top surface; and a plurality of granules disposed on the top surface of the polymer structure, wherein the combination of the granules and the polymer structure has at least about 40% energy transmissivity of solar radiation in the 400-750 nm wavelength range, the 650-1000 nm wavelength range, or the 450-1150 nm wavelength range.
 51. A method of modifying a surface of a photovoltaic device, the method comprising: disposing on the surface of the photovoltaic device a polymer structure, the polymer structure having a bottom surface and a top surface, the bottom surface being disposed on the surface of the photovoltaic device, the top surface having granules disposed thereon. 